The present invention relates to an improved cerebrospinal fluid ("CSF") shunt device, and, more particularly, to a CSF shunt which is capable of inspection and revision on a minimal invasive basis, thereby greatly reducing the pain and risk to the patient associated with previous shunt revision procedures. In addition, since the shunt revision can be performed on an out-patient basis, the cost of previous shunt revision surgical procedures is greatly reduced.
The valve regulated drainage of cerebrospinal fluid is an important neurosurgical intervention for the treatment of hydrocephalus, or "water on the brain." Hydrocephalus is caused by excess cerebrospinal fluid being located between the brain and skull. When congenital, hydrocephalus may result in excessive skull enlargement and, if untreated, progress to brain damage, or even death. When the condition occurs later in a person's life, the skull is no longer flexible and the condition can cause headaches, vomiting, and loss of coordination and mental functioning.
Hydrocephalus is commonly treated by providing a drain tube, known as a "shunt," between the source of the fluid within a ventricular cavity of the patient and another body cavity, such as the abdomen, chest, or vascular system (i.e., a major blood vessel, such as the jugular vein). Thus, in order to maintain the size of a child's skull at normal dimensions and to relieve pressure, the cerebrospinal fluid is drained or shunted to other parts of the body.
In order to install the shunt, a scalp incision is made and a small hole is drilled in the skull. The proximal end of the shunt is installed in the ventricular cavity. The distal end of the shunt is then installed in that portion of the body into which the cerebrospinal fluid is to be drained.
CSF shunts normally comprise a cannula or tubing system which is commonly fabricated from silastic, a material made by Dow-Corning. The ventricular or proximal end of the shunt is provided with small openings that vary from microns to millimeters in order to receive the cerebrospinal fluid into the shunt tubing. Likewise, the distal end of the shunt also is provided with small openings, often shaped as slits, to discharge the fluid from the shunt into the appointed body cavity. The shunts usually have an internal diameter of approximately 1.5 mm and are provided with a system of valves. The valves are generally one way, only allowing fluid to pass out of the ventricular cavity. Each valve is designed to open due to slight differential pressure between the inlet or proximal end of the shunt and its outlet or distal end. The valve will close in the event the pressure differential reverses, which may occur by coughing or straining of the patient, thereby preventing a reverse flow of blood or other fluid through the shunt into the ventricular cavity.
A typical CSF shunt is essentially L-shaped, except that it is installed in the skull of the patient in an inverted fashion. The shunt is comprised of various sections of tubing which are connected together. For example, the proximal or ventricular tube is inserted directly into the skull so as to be in communication with the ventricular cavity. This section of tubing is then connected, near the surface of the skull, to an elbow connector which forms a substantially 90.degree. angle. The elbow connector is in turn typically connected to another section of tubing which leads to a pump tube situated just under the skin of the skull. Finally, an outlet or drain tube is connected to the pump tube which allows drainage of cerebral spinal fluid to another body cavity. Thus, the elbow connector is near the "corner" of the shunt in that it conducts fluid out of the skull and down the body tangentially to the skull. A portal is also installed at the corner, just below the skin, to provide access to the shunt by a hypodermic needle. This portal allows the physician to withdraw fluid from or give injections into the tissue surrounding the shunt. A shunt exhibiting this configuration, including the function of the pump tube, is described in U.S. Pat. No. 3,654,932 to Newkirk, et al.
Due to the relatively small openings at the ends of the shunt and at the valves, the major complications associated with CSF shunting are obstruction, infection and valve malfunction. Because of the minimal internal diameter of the shunt, obstructions caused by protein globules, choroid plexus and other small particulate are common. Further, because of the location of the shunt and the fact that the tissue surrounding the shunt area receives little circulation, infection in this area is common. These problems require at least shunt revision, and often complete replacement. More importantly, any of these problems is life threatening and previously required major neurosurgical intervention, including hospitalization, general anesthesia and incisions that spanned three body cavities (cranial, thoracic, abdominal). In addition, the frequency of shunt obstructions is quite high, varying from 10% to 30% in most series. Approximately 35,000 new CSF shunts are inserted each year and most remain in place for life, unless replacement is required. Therefore, the expense, discomfort, and risk to the patient associated with previous shunt revision surgical procedures are substantial.
Accordingly, there is a clear need for a CSF shunt device which can be revised on a minimal invasive basis.